Readme / Dev setup instructions missing details

[cicorias]

• Detail which of Android Studio and SDK to install
• what API level is currently supported
• What JxCore -jxv level is currently supported.
• what is the right path for env vars: eg: export ANDROID_HOME=/<installation location>/Android/sdk doesn't exist
• Update: Ensure npm v3.x+ is NOT installed on Ubuntu

Required packages on Ubuntu:

sudo apt-get install lib32stdc++6
sudo apt-get install lib32z1

[artemjackson]

• Install latest Android Studio or android-sdk
  For Mac: brew install android-sdk
  It also sets your ANDROID_HOME correctly

• Current target level is android-21

• It's better to install latest version of jxcore (currently it is 3.1.2b)
  For Mac it can be dowloaded from here

• If you have already installed android-sdk the correct ANDROID_HOME sets automaticaly
  Otherwise set ANDROID_HOME to /<installation location>/android-sdk (or something similar that contains folders such platforms,samples,tools, etc ) and PATH to ${PATH}:$ANDROID_HOME/tools:$ANDROID_HOME/platform-tools
  E.g. on my machine it is

  export ANDROID_HOME=/usr/local/Cellar/android-sdk/24.4.1_1/
  export PATH=${PATH}:$ANDROID_HOME/tools:$ANDROID_HOME/platform-tools